Abstract Non-esterified fatty acids (NEFAs) play a central role in the development of type 2 diabetes and cardiovascular diseases (CVD). Although total fasting NEFAs have been associated with higher risks of diabetes, CVD, and mortality, no previous cohort study has examined of the associations of NEFAs measured after oral glucose challenge with cardiometabolic disease, despite their much stronger association with insulin sensitivity. Further, total NEFAs consist of >40 different fatty acids, and which subset of individual NEFAs or patterns of NEFAs confer the greatest risk of cardiometabolic disorders is currently unknown. In addition, although a large randomized trial has demonstrated the efficacy of metformin therapy and lifestyle intervention on diabetes risk, it is unclear what effects these have on individual NEFAs and whether reduction of serum NEFAs may account for their efficacy. These questions assume particular relevance in older adults, the group at greatest risk for cardiometabolic disorders. Our central hypothesis is that higher post-load NEFAs and atherogenic NEFA patterns can identify subjects at higher risk of cardiometabolic diseases and such abnormality can be favorably influenced by metformin therapy and/or lifestyle intervention. We will use prospective data from the Cardiovascular Health Study to examine the associations of post-glucose challenge NEFAs on the risk of cardiometabolic diseases (Aim 1) and evaluate associations of individual NEFAs (using an unbiased approach) and patterns of NEFAs (using current knowledge to derive NEFA patterns) with incident diabetes, atrial fibrillation, heart failure, and mortality (aim 2). Using data from the Diabetes Prevention Program, we will examine the effects of metformin therapy and lifestyle intervention on serum NEFAs collected 3 years apart. Our findings will shape our understanding of the role of NEFAs in diabetes and cardiovascular disease, and, given recent advances in NEFA receptor agonists, could identify potential drug targets for prevention of diabetes and its cardiovascular complications. Finally, our findings have the potential to harness low-cost and sustainable lifestyle interventions to address derangements in NEFA metabolism in elders, and extend some of the most important findings from our previous work in new directions in basic, translational, and population science.